In view of the speed limitations inherent in electronic circuits, all-optical data processing devices have become the focus of many research efforts. One category of such devices is the all-optical logic gate, which is deemed to be a main component in future integrated photonic circuits.
Some established techniques for achieving functional all-optical logic gates include: 1) use of integrated fiber based Mach-Zehnder interferometers (MZIs) that are often limited by back reflections of the optical signal, which are minimized by extending the cladding and substrate layers, as described for example in Y. Wu, T Shih, M. Chen, “New all-optical logic gates based on the local nonlinear Mach-Zehnder interferometer”, Optics Express, 2008 vol 16(1): 248-57; and M. Nazari, M. Haghparast, “Novel design of all-optical reversible logic gate using Mach-Zehnder interferometer in the field of nanotechnology”, Australian J. of Basic and App. Sci., 2011 vol 5(12): 923-9; 2) use of nonlinear optical processes in semiconductor optical amplifiers (SOA), such as four-wave mixing as described for example in Z. Li, G. Li, “Ultrahigh speed reconfigurable logic gates based on four-wave mixing in a semiconductor optical amplifier”, Photon. Tech. Lett., 2006 vol 18(12): 1341-3. D.; and cross-gain modulation as described for example in S. H. Kim, J. H. Kim, B. G. Yu, Y. T. Byun, Y. M. Jeon, S. Lee, D. H. Woo, S. H. Kim, “All-optical NAND gate using cross-gain modulation in semiconductor optical amplifiers”, Electron. Lett., 2005 vol 41(18); and 3) use of a combination thereof such as integrated Mach-Zehnder interferometers based on SOA as described for example in X. Ye, P. Ye, M. Zhang, “All-optical NAND gate using integrated SOA-based Mach-Zehnder interferometer”, Opt. Fiber. Tech., 2006 vol 12: 312-6.
SOA-based techniques are often limited by the carrier's recovery time, which, in turn, slows down the operation of the all-optical logic gate. In addition, these techniques often require the use of multiple SOAs to achieve functional all-optical logic gates, and fall victim to additional noise such as spontaneous emission noise as described for example in Wang, J., Sun, J., Sun, Q., “Experimental observation of a 1.5 μm band wavelength conversion and logic NOT gate at 40 Gbit/s based on sum-frequency generation,” Optics Letters, 2006 vol 31: 1711-3; and Wang, J., Sun, J., Sun, Q., “Proposal for all-optical switchable OR/XOR logic gates using sum-frequency generation,” IEEE Photonics Technology Letters, 2007, vol 19: 541-3.
Fiber nonlinearity-based techniques provide comparable functionality, without the limitations mentioned above. Among fiber nonlinearity-based logic gates, one of the techniques includes using the Kerr effect in highly nonlinear fibers (HNLF) to induce birefringence, thereby rotating the polarization state of an output light wave, which represents the optical gate operation with ultimate speed limitation above 100 Gb/s, as described for example in C. Yu, L. Christen, T. Luo, Y. Wang, Z. Pan, L. Yan, A. E. Willner, “All-optical XOR gate using polarization rotation in single highly nonlinear fiber”, Photon. Tech. Lett., 2005 vol 17(6): 1232-4; and C. Yu, L. Christen, T. Luo, Y. Wang, Z. Pan, L. Yan, A. E. Willner, “All-optical XOR gate based on Kerr effect in single highly-nonlinear fiber”, Conf. Lasers and Electro-Optics (CLEO), 2004 vol 2: 3-5.
However, long fiber lengths introduce polarization instabilities, which is one limitation of the aforementioned technique. A relatively short fiber length of 2 km was used to realise the XOR gate in C. Yu, L. Christen, T. Luo, Y. Wang, Z. Pan, L. Yan, A. E. Willner, “All-optical XOR gate using polarization rotation in single highly nonlinear fiber”, Photon. Tech. Lett., 2005 vol 17(6): 1232-4. Since polarization rotation is necessary in the papers of C. Yu cited above, presence of birefringence is another limitation of the technique, which may cause polarization mode dispersion (PMD) of the optical signal.
Therefore there is a need in the industry for the development of alternative improved all-optical logic gates, and for the development of the method and system for designing such improved all-optical logic gates.